AU777112B2

AU777112B2 - Thermoelectric power generator

Info

Publication number: AU777112B2
Application number: AU42756/01A
Authority: AU
Inventors: Mutsuko Hasegawa; Niichiro Hasegawa
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 2000-03-24
Filing date: 2001-03-22
Publication date: 2004-09-30
Anticipated expiration: 2021-03-22
Also published as: US6717043B2; WO2001071822A1; AU4275601A; WO2001071821A1; AU3327500A; US20020180042A1; JP3851168B2

Description

SPECIFICATION

TITLE OF THE INVENTION THERMOELECTRIC POWER GENERATION BODY BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a thermoelectric power generation body and more particularly to a thermoelectric power generation body capable of generating power not only from solar heat and geothermal heat but also from a heat source of medium or low temperature which has been impossible to be utilized by conventional arts, with high efficiency of thermoelectric conversion.

Description of the Related Art At the present time, heat energy is converted into electric power mainly by a heat engine in which the process is: heat energy -high pressure steam -turbine-generator-electric power.

This method of converting heat energy into electric power have greatly contributed as power sources for supporting people's life in society, but there is a problem that it accompanies a large waste heat with its thermal efficiency of 45% at the best.

To combine a gas turbine to this method has already been attempted to good purpose, and it is applicable to thermal power generation using fossil fuels but not applicable to nuclear power generation.

Power generation by fuel cells seems like a promising one from a point of view of largely improving thermal efficiency, at present the usable fuel is limited to hydrogen which is comparatively expensive and there still remain problems.

On the other hand, the conversion of heat energy into electric power using devices based on Seebeck effect is already established, but its thermal efficiency is 20 at the best and not in the state of general use on a large scale.

Electric power will continue without doubt to be necessary as an important energy to support people's life in society in the future. A requisite for the process of obtaining electric power from heat energy is to attain thermal efficiency as high as possible now that global environment crisis is strongly acknowledged.

However, there is a theoretical upper limit which can not be exceeded in thermal efficiency of each process of converting heat energy into electric power, and in any of the processes its thermal efficiency has reached near the upper limit by continued effort. Therefore, a leap in the concept of the method of thermoelectric conversion itself is necessary to get a quantum leap in thermal efficiency.

The inventors have investigated the operating mechanism of already-existing solar cells and devices utilizing Seebeck effect and worked toward development of a thermoelectric conversion device which operates at room temperature and moreover without large temperature difference in the device.

Two inventions made heretofore were applied for patent; the first one is disclosed Japanese Unexamined Patent Publication 6-151978 and the second is disclosed Japanese Unexamined Patent Publication 8-306964.

Q \OPERGCP%42756 rp doc-087V44 3- SUMMARY OF THE INVENTION In the present case, in order to appreciate the significance of the present invention, it is useful to describe a number of earlier studies made by the inventors.

These earlier studies are discussed briefly below.

The basic configuration of the thermoelectric power generation body according to the present invention is as follows:

(C)

Anode I Semiconductor I Cathode Basic operation is as follows: .y 1) Electrons are thermally excited in between energy bands 15 in the semiconductor.

2) When appropriate electric field exists in the semiconductor, the thermally excited electrons gather in region of conduction band and on the other hand positive holes gather in the region of valence 20 band. This is charge separation by the internal :electric field.

3) However, in the state cited above, the electrons and e positive holes are in the state of thermal equilibrium Soo: with Fermi level of region coinciding with that of 25 region If Fermi level of region can be raised to a higher level than that of region by use of some means, the electrons gathering in the region get energy to violate the thermal equilibrium state and flow through the circuit with load as electric current while accomplishing work against external load and arrive at region where the electrons meet with the positive holes, then again thermally excited in between the bands and return to region of conduction band, thus the current flow continues.

The heat energy used for thermal excitation in between the bands is converted into electric power by this process. A temperature difference between both poles is not necessary, which is different from the case of Seebeck effect. Therefore, as the heat energy flowed into the body does not flow out to anywhere but converted into electric power, thermal efficiency would be 100%. This is the idea of thermoelectric conversion that occurred to the inventors. The inventors have made repeated studies to realize the idea, and made several key inventions cited below.

The band gap of semiconductor is desirable to be equal or under 1 eV in order to induce the thermal excitation of electrons in between the bands at room temperature or a little higher temperature, which is well known. The condition for establishing an appropriate internal electric field to separate the carriers excited in between the bands is also publicly known. That is, in the configuration of an device shown below,

(C)

Anode I Semiconductor I Cathode the condition for establishing appropriate internal electric field to gather positive holes to region of valence band and electrons to region of conduction band is: with n-type semiconductor; A=OA d,(Eg-0.2)/q [i] adC=,-4 >0 [2] with p-type semiconductor; A A=d A -0p0 [3] A oc=oP- [4] where symbols denote 0 work function (v) Eg band gap (eV) q charge of an electron A position (A) C position (C) n n-type semiconductor p p-type semiconductor AN anode CA cathode.

The first idea the inventors hit upon as a means to establish Fermi level difference between region and is to increase minor carrier density in the plane of a semiconductor violating the thermal equilibrium state by external action.

The configuration of an device the inventors proposed as a means for realizing the idea mentioned above is that, tellurium (Te) is used as a semiconductor, copper (Cu) as an anode, aluminum (Al) as a cathode, The anode and cathode each is brought into close contact with the solid tellurium, and further glycerol is contacted to the cathode side. Properties of matter are as follows: Te: type of conduction p-type Eg 0.32 eV 0: Cu 4.86 V Te 4.70 V Al 4.25 V.

These values of properties suffice the required conditions[3] and Further, electrons are separated due to the reaction of Al having high reactivity with glycerol and the electrons are implanted into tellurium (Te) at the cathode.

According to the idea of the inventors, the electrons, which are minor carriers in tellurium externally implanted with high potential level exceed the equilibrium state in both energy level and density, and would raise the Fermi level in region The idea was verified by the experiments and the inventors disclosed it in Japanese Unexamined Patent Publication 6-151978.

Though the invention enabled the device thermoelectric conversion, further increase of output was required.

Further, crystalline semiconductor such as tellurium is not suitable for producing a sheet-like semiconductor of large area.

Producing a semiconductor in a sheet of large area is necessary for mass production of thermoelectric power generation body, and a semiconductor suitable for this object should be selected.

The inventors hit upon an idea of using sulfide semiconductor.

This is based on the characteristic that sulfide semiconductor is of ionic bonding and a semiconductor which functions well can be obtained by a comparatively easy production method. An idea of producing a sheet of large area utilizing the characteristic is that the fine particles of sulfide semiconductor obtained by liquid phase reaction at normal temperature shaped into a solid matter and hardened using an appropriate carrier material and binder.

It is necessary that the sulfide semiconductor is in the state containing water moderately, and the fact that it contains water achieves an important role as mentioned later. The electron affinity x of sulfide semiconductor was assumed to be 3.6 3.8 V, and further the following materials and the like which were semiconductors having band gap Eg of equal or smaller than 1 eV were selected as construction elements of the device: Cu 2 S(p-type, assumed Eg=0.6 eV) FeS (n-type, assumed Eg=0.7 eV) The output of the device mentioned before using tellurium as semiconductor is small because of small difference of Fermi level between region and It was recognized that this is the constraint which the method of making the density of minor carriers higher than that of the thermal equilibrium state has.

Thus, an idea occurred to the inventors was: electrochemical reaction having low reaction potential on vacuum basis is allowed to exist steadily in region on the other hand electrochemical reaction having high reaction potential on vacuum basis is allowed to exist steadily in region the difference of both reaction potentials is applied to the semiconductor as forward bias voltage; and a large difference in Fermi level is established between region and Here exist two preconditions. The first is that the reaction potential generated in region and that generated in region should be linked. To realize the linkage, the semiconductor layer existing between region and is required to be in the state of containing water. A semiconductor containing water is attained only by the method, as mentioned above, in which fine particles of semiconductor are reduced to a solid body while containing water. A crystalline semiconductor can not address this requirement.

The second is that excessive diode current should not flow in the state the forward bias is applied. This is attained by allowing sufficiently high schottkey barrier to exist in region or allowing potential barrier due to p-n junction to exist in the central region between region and In the thermoelectric power generation body prepared by this method, the potential barrier existing internally for separating the thermally exited carriers between bands contributes advantageously to restrain the diode current.

The inventors began by selecting a redox reaction system composed of awater solution of {Cu+(NH 3 2 -Cu 2 (NH, 2 1, The reaction potential of this reaction group exists in the favorable region as follows:

E

O 0.06 V vs NHE (Hydrogen electrode potential basis) (where n=2) PA -4.49 V vs Vacuum Further, the reaction system has charge transport ability as a characteristic of redox reaction, which is also a preferable feature.

Then, the inventors thought of allowing the following reaction system to exist in the equilibrium as a reaction to be allowed to steadily exist in region by using as cathode a metal having strong affinity with S 2 which is an anion constituting the semiconductor: Cathode material S 2 <Sulfide 2e- It is in the state the liberated electrons by the reaction are taken away that the reaction proceeds rightward in the above reaction, so the equilibrium can be kept if isolated existence of electron demanding reaction center is not allowed to exist in the reaction system. Although a redox reaction system includes electron demanding reaction, electrons are not completely absorbed substantially or irreversibly as long as the balance is sustained between reduction reaction and oxidation reaction.

The reaction potential difference obtained by linking electrochemical reaction in region and that in region (C) is sufficiently large as shown in Table 1.

(Table i) Cathode 21 v Cathode E(V vs NHE) lc (V vs Vac.) A b C -1A (V) material Cu -0.89 -3.54 0.95 Fe -0.965 -3.47 1.02 To provide a redox reaction system to an anode side is well known in the art of wet-type solar cell. However, the finding that Fermi level difference is established by allowing reaction potential due to electrochemical reaction to exist at both the anode side and the cathode side and the application of the difference of the both reaction potentials to a semiconductor layer as a forward bias voltage is a new one obtained by the inventors, by which new ground of utilizing the thermal excitation phenomenon for a thermoelectric conversion was broken. The inventors have applied for patent with a series of the inventions mentioned above as disclosed in Japanese Unexamined Patent Publication 8-306964.

However, there remained a problem that the corrosion of cathode material should be deterred in the method according to Japanese Unexamined Patent Publication 8-306964. The corrosion is caused by the fact that the redox reaction liquid existing in the anode region osmoses gradually into the semiconductor layer and intrudes into the cathode region where it reacts with the cathode material. As a natural result, the damage of cathode deteriorates the durability of the device.

To cope with this problem, the inventors tried at first to lower the permeability of the semiconductor layer as low as possible but did not succeed in sufficing at the same time two mutually contradictory requirement, i.e. to link the reaction potentials generated at the both planes of the semiconductor layer and to decrease the permeability of the layer.

As a next approach, the inventors hit upon an idea in that the water solution of (Cu (NH) 2 -Cu 2

(NH)

2 n(n=0, i, 2))is occluded in a suitable adsorbent, a necessary amount of binder is added, and further a sufficient amount of ammonium salt is added for the reason mentioned later to solidify and harden the reaction liquid for depriving it of fluidity in order that no reaction liquid may intrude into the cathode range.

The inventors found that activated carbon shows an extremely superior performance among a variety of existent adsorbent and succeeded in solidifying redox reaction liquid.

Further, the electrolytic water solution room was eliminated from the cathode region in correspondence with the solidification of the anode reaction liquid, because if Q "p(erp42756c doc-404= 4 11 electrolytic water solution remains in the cathode range the liquid intrudes into the anode region to allow the elution of the redox reaction system solidified resulting in the loss of effect of the solidification.

In summary, the invention provides a thermoelectric power generator comprising a thin plate of solidified fine and hydrated particles of a sulfide semiconductor in contact with an electrochemical reaction having a lower Fermi level on a side and in contact with an electrochemical reaction having a higher Fermi level on an opposite side, wherein the electrochemical reaction having the lower Fermi level is a first solidified redox reaction system comprising an aqueous solution of {Cu+ (NH 3 2

~C

2

(NH

3 2+n 1,2) or Ni2+ (NH 3 6 carried on electrically conductive adsorbent and bound with hydrophilic organic polymer and hemihydrated gypsum.

The inventors thus succeeded in generating large output in continuation by the thermoelectric power generation body in which a solidified redox reaction system is provided in the region of an anode and further the region of a cathode 20 is reduced to the semi-dried state where the cathode Scontacts a semiconductor. Moreover, this solid state construction is simple, free of trouble such as leakage of liquid, and suitable for commercialisation. The invention cited above is the skeleton of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 is a schematic representation showing the structure of a device with the solidified redox reaction structure of a device with the solidified redox reaction Q %OPRGCPU2736 rp doc-0W07M4 11A system exposed to the atmosphere in the first embodiment.

Fig. 2 is a conceptual rendering for explaining the transfer of electrons and the change of potential in a device according to the present invention.

Fig. 3 is a schematic representation showing the configuration of the device in the second embodiment.

Fig. 4 is a schematic representation showing the configuration of the device in the third embodiment.

Fig. 5 is a schematic representation showing the construction of a device of the first comparative example in which the redox reaction system is liquid phase and cathodes are spider coils immersed in glycerol.

a..

a .r 9

"I,

9S 9 5," 99 99 9 99 9 9 9 9 9* 9 9* *9**99.9 9 99* 9. 99 99 99 9 FIG.6 is a schematic representation showing the structure of a device of the second and third comparative examples with the solidified redox reaction system isolated from the atmosphere.

Reference numbers in the drawings denote: 11 is an anode(corrugated thin plate of platinum), 12 is a jig for holding the anode, 13 is a solidified redox reaction system, 14 is a sulfide semiconductor, 15 is a cathode( thin plate of pure iron), 21 is an anode(thin plate of platinum), 23 is a solidified redox reaction system, 24 is a sulfide semiconductor, is a cathode(thin plate of pure iron), 1 is a circuit with load, 0 is a supplementary circuit, R, is a resistance of load,

R

0 is a resistance for adjustment, E 0 is a supplementary power source, 31 is an anode(thin plate of graphite), 33 is a liquid state redox reaction system, 34 is a sulfide semiconductor and is a cathode(spider coil-like thin wire immersed in glycerol).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The action in a device of the present invention will be explained hereinbelow. As mentioned before, water solution of {Cu (NH 3 2 -Cu 2

(NH

3 2 1, has two roles to perform as redox reaction system, that is, to generate reaction potential and to transfer electric charge.

Among them, the charge transfer is expected to be performed by the diffusion of cations in the form of Cu'(NH 3 2 and Cu 2

(NH

3 2 in the water solution, and it is supposed that the charge transfer ability is lost in the state the cations are fixed on the adsorbent and as a result reaction potential generation ability is also lost, but wonderfully, in the actual system using activated carbon as adsorbent, the charge transfer ability increased on the contrary and reaction potential generation ability was also raised.

The next thing the inventors learned was that the solid body which consists of activated carbon powder adsorbing and holding the redox reaction liquid and is hardened using burnt gypsum as binder maintains a steady reaction state only when it receives the action of oxygen. When the action of oxygen can not be experienced, electric conduction ability of the redox reaction system decreases with time, and the output of the thermoelectric power generation body decays. It was recognized that such need of oxygen is not a peculiar problem to a solidified redox reaction system, it is also a problem to the water solution and is a phenomenon intrinsic to the redox reaction system of {Cu'(NH) 2 -Cu 2 (NH 2 1, To maintain a steady state in the redox reaction system, it is necessary that both densities of reduction type cations Cu*

(NH

3 2 and oxidation type cations Cu 2

(NH

3 are in a steady state.

Oxidation reaction is: Cu' (NH 3 2 nNH 3 Cu' (NH 3 )2+n e Reduction type reaction is: Cu 2

(NH

3 )2, n e- Cu (NH 3 nNH 3 In the state either of the reactions proceeds dominantly, there arises inevitably uneven mass distribution of reaction matter and the steadiness of reaction will be lost. Here the inventors focused attention on the point that the occurrence of the reaction is influenced by the value of n of an oxidation type cation Cu 2

(NH

3 2 recognized the importance of maintaining high value of n, and investigated thoroughly the condition of realizing it to obtain new findings.

Gibbs generation energy concerning the complex ion in the water solution is obtained from the table of constant of properties as follows: Cu' (NH 3 2

AG°

29 8 -65.01 kJmol- 1 Cu 2

(NH

3 2 -30.49 Cu 2

(NH

3 3 -73.17 Cu 2

(NH

3 4 -111.33 Calculation results of oxidation reaction potential of reaction Cu* (NH 3 nNH 3 Cu 2

(NH

3 e- using above cited values are shown in Table 2.

(Table 2) n AGR.

29 (kJ) E 0 (V vs NHE) 0 33.77 0.350 1 17.66 0.183 2 6.06 0.063 It is recognized from this table that, reduction reaction proceeds dominantly over oxidation reaction when n is small and when n=2 oxidation reaction becomes easy to occur balancing with reduction reaction. Therefore, it is necessary to keep n=2 in order to attain a steady state of reaction system. Essentially reaction Cu 2

(NH

3 2 Cu 2

(NH

3 2 nNH 3 is an equilibrating reaction, and if the density of NH 3 in the vicinity of Cu 2

(NH

3 is sufficiently high, the state of n=2 is maintained. On the other hand, when the density of NH 3 becomes lower than that of equilibrium state, the value of n decreases resulting in uneven distribution of reduction type complex ion Cu* (NH 3 2 Oxygen takes on the task of reducing unevenly distributed Cu'

(NH

3 2 to Cu 2

(NH

3 2 by oxidation. The reaction is as follows: H,0 1/20, 2e- 20H- E 0 0.401V vs NHE t Cu' (NH 3 +nNH 3 Cu2+ (NH 3 +e- If OH- formed here is left to remain as it is, it intrudes into the cathode region to corrode the cathode and moreover allows dielectric hydroxide to be formed on the electric conduction face of the cathode, which is unfavorable. Therefore, OH- should be eliminated in the redox reaction system. This is done by the reaction NH, OH NH 3

H

2 0. So, it is necessary to allow a sufficient amount of ammonium salt, ammonium chloride or ammonium sulfate to coexist as reaction material beforehand in the redox reaction system. Advantageously, NH 3 formed like this contributes to maintaining high density of NH 3 in the vicinity of Cu 2

(NH

3 4 As mentioned above, the action of oxygen is important, and the inventors thought up to open the anode room to the atmosphere and to secure a large surface area of the redox reaction system in order to make it easy for the system to receive the action of oxygen.

Thus, the steady maintenance of the density of Cu 2

(NH

3 4 is made possible in the solidified redox reaction system having a large surface area for easy reception of action from the atmosphere, in which the water solution of {Cu (NH 3 2 -Cu 2

'(NH

3 2 i, is carried on activated carbon and ammonium salts is added. It is supposed that the activated carbon acts as catalyst to help the action of oxygen and further as adsorbent to hold NH3.

A thermoelectric power generation body provided with the solidified redox reaction system according to the idea and invention described above generates output exceeding that of a thermoelectric power generation body provided with a liquid state redox reaction system without accompanying the damage of cathode due to corrosion. This will be shown in comparison of the first, second, and third embodiments with the first comparative example.

Although the problem of excessive OH- can be solved as mentioned above, the inventors cannot but pay attention to the fact that there remained the problem that electron demanding action by the reaction of H 2 0 1/202 2e 20H- promotes electron liberation reaction at the cathode and consumes the cathode due to the action of chemical cell.

Cathode reaction is as follows: Fe S 2 FeS 2e- E -0.965 V vs NHE Fe Fe 2 2e- E 0 -0.440 V vs NHE Reaction steadily exists in region breaks the equilibrium of [FeS"- S2-" Fe cathode] bearing the task of generating high reaction potential and conducting electrons, and consumes S2- of finite amount. On the other hand, reaction occurs after reaction proceeds no longer, in which Fe 2 formed therein deteriorates the electron conduction ability between FeS and Fe. The secondary reaction like this is of a kind which is accompanied due to the existence of the process of substantially absorbing electrons in a redox reaction system.

Therefore, to allow only the reaction of H 2 0 1/202 2e to achieve desired action and not to allow absorption of electrons in a redox reaction system has become the next challenge.

The inventors solved the problem through achieving a balance between giving and receiving of electrons in a redox reaction system by adding to the solidified redox reaction system an oxidation electrode which is energized by an auxiliary power source to allow the reaction of 20H--H 2 0 1/202 2e- to occur.

This will be explained in reference with an example of the thermoelectric power generation body according to the present invention shown in FIG.3. In the drawing, a thermoelectric power generation body is a cell configured so that a solidified redox reaction system and a solidified redox having a direct connection region with the solidified redox reaction system on its one side and contacting a sulfide semiconductor on the other side sandwiches an electrode for oxidation, and the face of the sulfide semiconductor not contacting the solidified redox contacts a cathode. A voltage E 0 is applied between the electrode for oxidation and the cathode by an auxiliary power source via an adjusting paper resistance R 0 and a supplementary power circuit 0. The output power can be taken out by connecting a load circuit 1 with a load resistance R1 between the cathode and anode.

i) The solidified redox reaction system is given gas permeability to make the transmission of oxygen easy and following reactions are allowed to occur in region and In region H 2 0 1/20, 2e" In region 20H- H 2 0 1/202 2e- In region H 2 0 1/202 2e-

T

RED OX* e ii) The solidified redox reaction system is given non-permeability of 02 and resistant property to permeation of OH-, to prevent the transfer of these activated matter.

iii) By providing the direct connection range of the solidified redox reaction systems and the low potential generated in the reaction system is transferred to the reaction system to maintain the potential of the reaction system to a low level, by which the density of reduction type complex ion and that of oxidation type complex ion are maintained in an appropriate relation.

iv) The electrons liberated at the cathode flows into the redox reaction system as diode current. The electrons have high potentials and have the possibility of exerting the destructive reduction action to the redox reaction system as follows: Cu' (NH 3 2 e- Cu 2NH 3 (Aq) Eo -0.12 V vs NHE Therefore, it is required to reduce the reaction system (B) to a complex ion species which is resistant to destruction. Here, the inventors paid attention to Ni2+(NH 3 6 The destructive reduction reaction of this complex ion is well known.

Ni2(NH 3 2e- Ni 6NH 3 (Aq) Eo -0.49 V vs NHE This complex ion is far the more resistant to destruction than Cu (NH 3 2 However, whether Ni 2

(NH

3 6 exhibits redox reaction behavior or not could not be found in literatures.

[Ni(CN)4]' 3 -[Ni(CN)4] 2 is known in a redox reaction system which Ni ion forms, and this is the change of Ni< Ni 2 e-.

On the assumption that a complex ion group with NH 3 also exhibits redox reaction behavior, the inventors assumed as: Ni'(NH 3 6 Ni 2

+(NH

3 6 e- E 0 -0.2 V vs NHE v) The following reaction is known as redox reaction which does not suffer destructive reduction: [Fe(CN),] 3 e- [Fe(CN),] 4 E -0.36 V vs NHE The destructive reduction reaction of this complex ion species is [Fe(CN) 6 4 2e- Fe 6CN E 0 -1.8 V vs NHE and this reaction does not occur by the electrons liberated at Fe cathode. Therefore, the reaction system can be said to be superior concerning the two points mentioned above. However, [Fe(CN) 6 generates nascent oxygen when meeting with an alkali by the following reaction and adversely affects against the sulfide semiconductor and Fe cathode.

2[Fe(CN)] 3 20H- H 2 0 O vi) In view of the circumstances mentioned heretofore, the inventors obtained a finding that it is suitable to make the redox reaction system non-permeable to gas and OH- by using [Fe(CN) 6 4 as complex ion and filling fine spaces in the layer with a binder consisting of organic polymeric matter when solidifying the system to be mounted on the thermoelectric power generation body. Thus, the invention as shown in FIG.3 was completed. A concrete example will be described later as embodiment example 2.

Next, the inventors investigated concerning what the peculiar action of activated carbon arises from and obtained further findings. The thermoelectric conversion according to the present invention is possible by the interlocking of adjoining redox reaction system and semiconductor as shown in FIG.2. In FIG.2, symbols denoted as follows: RED reduction type complex ion OX* oxidation type complex ion thermal excitation between bands electron separation 7P redox reaction potential 7c cathode reaction potential The redox reaction system bears the role of electric conduction and generation of low reaction potential, the semiconductor bears the role of thermal excitation between bands and succeeding separation of electrons.

The inventors ascertained that the rate-determining factor is the rate of redox reaction in the redox reaction system in which the regulating factor of flow rate of the electrons transferring from interface A to interface C is the reaction rate in the redox reaction system and the thermal excitation rate between bands and diode electron flow rate in the semiconductor. With this being the situation, the inventors succeeded in generating a large electric current without using activated carbon by adding a direct electron conduction passage by dividing the roles such that the main role of the redox reaction system is to generate low reaction potential and that of the direct electron conduction passage is the transfer of electrons. This relation is shown in the fourth embodiment example and the third comparison example.

Thus, it was clarified that it was due to the large contribution of the electric conductivity of the activated carbon that the powdered activated carbon made the generation of the large electric current possible. Actually, testerprobes were inserted in powdered activated carbon of Kanntou Chemicals Ltd. make used in experiments to measure resistance, and 0.8 kQ was measured when the distance of the probes is 1 cm.

In the case the role of reaction potential generation and the roll of electron transfer are divided as in the present invention, since the adsorbent of redox reaction liquid need not have electron transfer ability, any of general-purpose adsorbent such as activated carbon, charcoal, silica gel, molecular sieve, and burnt gypsum may be adopted, and further soccer ball-like carbon which is new material can be used as well. It is permissible to select among them a material having the strongest adsorbing ability for the complex ions composing the redox system Here, the adsorbing ability means adsorption density and fixing strength.

As material for bearing the role of electron conduction, platinum, gold, graphite, etc. having high electrochemical stability are suitable. The material should be allowed to coexist in the redox reaction system in the form of flocculus, net, or chip. Aside from this, Cu 2 S which is a p-type semiconductor may be used as electrode material.

The inventors investigated concerning the method for reducing the adverse effect of diode current. The diode current should be minimized as mentioned before since it induces the destructive reduction of the redox reaction system. On the other hand, it is well known in a crystal semiconductor that the diode current is reduced to a small value by pn junction.

Based on this fact mentioned above, the inventors made an aniso type hetero junction body with p-type Cu 2 S of sulfide semiconductor in a state of cluster of fine particles and n-type FeS, and attained the desired result.

Specifically, Cu 2 S is provided instead of the solidified redox reaction system in the thermoelectric power generation body configured as shown in FIG.3. In this case, it is necessary to produce the state having non-permeability of gas and OH- by adding a binder consisting of organic macromolecular matter the same as in the solidified redox reaction system The result of power generation by the thermoelectric power generation body of this type is shown in the third example.

The inventors also takes note of the fact that there are two significant meanings in removing the water solution of electrolyte from the cathode region.

In a thermoelectric power generation body configured in the following form:

(C)

Anode Solidified Sulfide Cathode redox reaction system semiconductor only that the lower reaction potential generating at interface is connected with the higher reaction potential generating at interface by the medium of the semiconductor is necessary, and that the redox reaction system and the cathode form a chemical battery is not necessary. On the contrary, the chemical battery is harmful and should be eliminated.

It is useful for suppressing the re-elution of water solution from the solidified redox reaction system as mentioned before and also for suppressing the advancing of chemical battery action as mentioned above not to provide the room of the water solution of electrolyte in the cathode region. However, if the cathode contact is entirely dry, reaction potential is not generated.

By impregnating glycerol or glycerol with water added in region instead of the water solution of electrolyte, continuous power generation has become possible.

The basic operation for realizing thermoelectric power generation the inventors conceived and invented will be wholly summarized hereinbelow.

The first operation is to allow the thermal excited electrons between bands in a semiconductor to gather to the region of cathode contact of the conduction band, on the other hand, positive holes in the valence band to gather to the region of anode contact. This action can be realized by allowing the semiconductor to contain an appropriate electric field in it.

The second operation is to allow a higher fermi level of cathode region than that of anode region by giving to the carriers gathering to both planes of the semiconductor the energy or density or both of them for the carriers to violate the equilibrium.

The first means for realizing this is the method in which electrochemical reaction is allowed to exist in either plane of the semiconductor and the density of minor carrier on the plane is increased to violate the equilibrium.

The second means is the method in which electrochemical reaction having lower reaction potential on the vacuum basis is allowed to exist in the anode side, on the other hand that having higher reaction potential on the vacuum basis is allowed to exist in the cathode side, and the potential difference of both reactions is applied to the semiconductor as forward bias voltage. As to the power output, the second means is overwhelmingly superior.

The third operation is to select a large area sheet-like semiconductor which is suitable for realizing the first and second operation and also suitable for mass production of the thermoelectric power generation body. This can be realized by forming and hardening wet, fine particles of sulfide semiconductor by use of appropriate binder and carrier.

The fourth operation is to suppress the corrosion of cathode induced by the intrusion of reactive matter in the cathode range by allowing suitable adsorbent such as activated carbon to carry the water solution of the reactive matter, thus solidifying the redox reaction system used as generating source of the lower reaction potential necessary for the anode side.

The fifth operation is not to allow the chemical battery reaction to proceed between the electrochemical reaction at anode side and that at cathode side in the thermoelectric power generation body formed by the second means of the second operation. It is important not to allow substantial absorption of electrons to occur in the redox reaction system, since, if the substantial adsorption of electrons occurs in the redox reaction system acting at the anode side, which induces the liberation reaction of electrons and allows the chemical battery reaction to proceed. The auxiliary oxidation electrode provided in the redox reaction system works to achieve this.

Further, it is also important that the range of anode and cathode are linked by ions and the transfer of the ions is suppressed.

Thermoelectric power generation is possible when the first and second operation among the five operations are established at the same time. However, the attainment of practicability requires the establishment of the whole operations from the first to the fifth at the same time.

By the way, the inventors cited in the first application, Japanese Unexamined Patent Publication 6-151978, mainly about the first operation and the means for realizing the operation, and concerning the second operation, the first means is mentioned only slightly.

The first operation and the means for realizing the operation are publicly known, however, the idea of utilizing them for a thermoelectric power generation body was a fresh one at the time and it is thought to be meaningful that examples of devices realizing the second operation are disclosed in the application.

The inventors described extensively concerning the second means of the second operation and the third operation in Japanese Unexamined Patent Publication 8-306964. The inventor's understanding of the essence of action was unripe at the time, although they had recognized rightly concerning the means for solving the problem. The present invention opens the way to practical use of a thermoelectric power generation body by cultivating a better understanding on the essence of action in the second operation and adding the forth and fifth operations.

(The first example) The solidified redox reaction system 13 was formed by allowing the saturated water solution of {Cu (NH 3 2 -Cu 2

(NH)

2 1, 2)1 to be adsorbed to a proper amount of activated carbon powder to be made into a state of coagulated powder without free liquid phase, adding a small amount of burnt gypsum, a proper amount of crystal grains of ammonium chloride, and glycerol added with water to reduce the coagulated powder to a slurry to be poured into a determined mold and hardened. A large number of pores was made to increase surface area in the process of hardening.

FeS 14 was formed by adding S 2 in the form of water solution of 15 wt% of K 2 S to a determined amount of crystal grains of FeSO, 7H 2 0 so that the equivalence ratio of S 2 -/Fe 2 was 0.90 to cause raction. A small amount of ZnCl 2 powder was added to the obtained colloidal reaction product to fix the remaining free S 2 as ZnS.

The preparation of these sulfides was done in an atmosphere without air or preferably in inert-gas atmosphere.

A proper amount of burnt gypsum was added as hardening agent to the reaction product to reduce it to slurry. The slurry was carried on water retaining papers of determined size, then determined numbers of sheets of the papers were overlapped, pressed, and hardened.

The electric conduction type of the FeS prepared by this method was determined as n-type from the measurement of Seebeck effect.

A small amount of glycerol was allowed to permeate in the cathode range of FeS. The action area of the FeS layer provided on the device was consistently 4 cm 2 The cathode 15 was a thin plate of pure iron contacting FeS 14 prepared by the method mentioned above in accordance with the determined arrangement as shown in FIG.1 showing the construction of the device. Then, the solidified redox reaction system 13 was brought into contact with FeS 14 and the anode 11 of corrugated platinum thin plate was brought into contact with the redox system 13 using the anode holding jig 12 so that part of the solidified redox system 13 was exposed to the atmosphere. Then they were tightened together from outside to complete the assemblage of the device.

The power generation performance (under operation temperature of 40 45 cC) of a device thus prepared is shown in Table 3, and slight cathode corrosion was observed.

(Table 3) Breakaway voltage 0.83 0.86 V Attenuation after Load resistance( Output(mW) continuous generation for 5 Hrs.

330 1.5 No attenuation 170 2.7 No attenuation 3.9 Slight attenuation (The second example) The solidified redox reaction system 13 was formed according to FIG.3 by coupling reaction system of {Cu(NH 3 2 -Cu 2

(NH

3 )4 and reaction system of Ni 2

(NH

3 6 At first, reaction system was prepared by adding a determined amount of activated carbon powder to the water solution of Ni 2

*(NH

3 6 and mixing sufficiently, then adding a determined amount of burnt gypsum and water and mixing sufficiently.

Then, after adding a bond for wood working and mixing sufficiently, the obtained slurry-like mixture was poured into a determined mold and hardened. A bond for wood working or the like was filled in the gap developed between the mold and the mixture due to the shrinkage of the hardened mixture. After completion of this process, the supplementary platinum electrode for oxidation was installed and the frame for reaction system was fitted.

Then, a determined amount of ammonium chloride was added to the saturated water solution of {Cu*(NH 3 ),-Cu 2

(NH

3 4 a proper amount of activated carbon powder was added and mixed sufficiently, after that a determined amount of burnt gypsum and water was added and mixed sufficiently to reduce the mixture to a slurry state. The slurry was poured into a mold prepared beforehand and hardened.

Here the area of the supplementary platinum electrode should be smaller than that of the electric conduction plane of the redox reaction system to secure the direct connection region of reaction system with reaction system Next, FeS 14 was formed by adding S 2 in the form of water solution of 15 wt of K 2 S to a determined amount of crystal grains of FeSO4 7H 2 0 so that the equivalence ratio of S 2 -/Fe 2 is 0.90 to cause reaction, and adding a small amount of ZnCl 2 powder to the colloidal reaction product obtained to react with the remaining S 2 The preparation of these sulfides was done in an atmosphere without air or preferably in inert-gas atmosphere.

Then, after a determined amount of burnt gypsum was added and mixed sufficiently, the reaction product was carried on water retaining papers of determined size wetted with ethanol anhydride, required numbers of sheets of the papers were overlapped, pressed, and hardened.

The cathode 15 made of a thin plate of pure iron and the anode 11 made of a corrugated thin plate of platinum were used, the redox reaction system 13 respectively by using the anode holding jig 12 such that part of the redox reaction system 13 was exposed to the atmosphere, and the assemblage of the device was completed by tightening them from outside.

The power generation performance under operation temperature of 37 41 oC of the device thus prepared is shown in Table 4. No cathode corrosion was observed.

(Table 4) Breakaway voltage 0.72 0.75 Current(mA); Load resistance: 85Q 5.3 Power Load resistance: 85Q 2.4 Quantity of electricity(Coulomb) 490 Supplementary current(mA) 0.25 Attenuation after continuous No attenuation generation for 25 Hrs.

(The third example) The thermoelectric power generation body was composed as shown in FIG.4.

At first, Cu 2 S layer was formed. S 2 in the form of water solution of 15 wt% of K 2 S was added to a determined amount of CuCl powder for reaction so that the equivalence ratio of S2-/2Cu* was 1.0, filter paper was pushed against the reaction product to dehydrate. The preparation of these sulfides was done in an atmosphere without air or preferably in inert-gas atmosphere.

A determined amount of burnt gypsum was added to the obtained cake and mixed, further a determined amount of a bond for wood working was added and mixed sufficiently. The obtained viscous liquid was filled in a determined mold and hardened. As the hardened substance shrank in the mold to develop a gap between them, a bond for wood wprking was filled in the gap.

The supplementary platinum electrode for oxidation was installed to the Cu 2 S layer and the frame for the redox reaction system 13 was fitted. Here the area of the supplementary platinum electrode should be smaller than that of the electric conduction plane of the Cu 2 S layer to secure the direct connection region of the redox reaction system with Cu 2

S.

The redox reaction system 13 of {Cu(NH 3 2 -Cu2(NH) 4 was formed by the same process as in the second example.

FeS 14 was formed also by the same process as in the second example. The cathode 15 was installed, the anode 11 was attached by the medium of the holding jig 12 so that part of the redox reaction system 13 was exposed to the atmosphere, and finally they were tightened from outward to complete assemblage.

The power generation performance (under operation temperature of 37 41 C) of the device thus prepared is shown in Table 5. No cathode corrosion was observed.

(Table Breakaway ,voag 0.78 0.80 Current(mA); Load resistance: 45Q 9.2 Power Load resistance: 45Q 3.9 Quantity of electricity(Coulomb) 460 Supplementary current(mA) 0.33 Attenuation after continuous No a No attenuation generation for 15 Hrs.

(The fourth example) The solidified redox reaction system 23 was formed by allowing the concentrated water solution of Ni 2

+(NH

3 6 to be adsorbed to a proper amount of charcoal powder to be made into a state of coagulated powder without free liquid phase, adding and mixing a large amount of graphite chips(about 3mmX3mmX 0.38mmt), and filling the mixture in a determined mold.

FeS 24 was formed as in the first example.

A thin plate of pure iron and a thin corrugated plate of platinum was used as the cathode 25 and anode 21 respectively.

Each component was arranged and brought into contact with other element in accordance with FIG.1 showing the construction of the device and tightened from outward to complete the assemblage of the device.

The power generation performance (under operation temperature of 40 45 C) of the device thus prepared is shown in Table 6.

(Table 6) Breakaway voltage 0.47 0.50 V Load Attenuation Load ta Output(mW) after continuous generation for 2 Hrs.

0.60 Slight attenuation (The first comparative example) The saturated water solution of {Cu'(NH 3 2 -Cu2+(NH 3 2 1, was used as the redox reaction system 33. It was poured into the liquid room of the liquid phase redox reaction system of the device configured as shown in FIG.4 with its upper part open to the atmosphere.

FeS 34 was formed by adding S 2 in the form of water solution of 15 wt of K 2 S to a determined amount of crystal grains of FeSO 4 7H 2 0 so that the equivalence ratio of S2-/Fe2+ is 0.90 to cause reaction. A small amount of ZnC1, powder was added to the obtained colloidal reaction product to fix the remaining free

S

2 as ZnS. The preparation of these sulfides was done in an atmosphere without air or preferably in inert-gas atmosphere.

A bond for wood working of 1.2 times in volume was added to the obtained reaction product and mixed. The obtained viscous slurry was carried on water retaining paper of determined size, required numbers of sheets of the paper were overlapped, pressed, and hardened. The hardened solid body was installed in a chamber made of rubber plate, and the periphery of the solid body was glued to the chamber with a bond for wood working so that no gaps were remained. The reason a bond for wood working was used is to prevent the permeation of reaction liquid by filling vacant spaces and to allow the FeS layer to be moist to the minimum extent required.

A thin wire of pure iron wound in a spiral coil was used as cathode 35 which was immersed in glycerol in the cathode room of the device constructed as shown in FIG.5. By this the redox reaction liquid is difficult to transfer to the cathode room.

A thin plate of graphite was used as anode 31, and the device was assembled by the same method as in the first example as shown in The power generation performance (under operation temperature of 40 42 t) of the device is shown in Table 7.

However, the corrosion of cathode occurred considerably when the generated quantity of electricity was 750 coulombs. However, the amount of corrosion was far small compared with that estimated in correspondence with the generated quantity of electricity.

(Table 7) Breakaway voltage 0.63 V Load Attenuation Load resistance(Output(mW) after continuous resistance _generation for 5 Hrs.

68 1.7 Almost no attenuation 1.7 Slight attenuation (The second comparative example) The different point from the first example was only that the solidified redox reaction system was shut off from the atmosphere, the conditions other than that were the same as in the first example. The construction of the device is shown in FIG.6. The power generation performance (under operation temperature of 45 C) of the device is shown in Table 8.

(Table 8) Breakaway voltage 0.83 V d Attenuation Load ta Output(mW) after continuous generation for 5 Hrs.

330 1.4 Considerable attenuation (The third comparative example) A concentrated water solution of Ni 2 (NH 3 6 was used as original liquid for the solidified redox reaction system 23. The solution was adsorbed to a proper amount of charcoal powder to reduce the solution to a state of coagulated powder without free liquid phase. Then a proper amount of burnt gypsum and water was added to reduce the coagulated powder to slurry. The slurry was poured into a determined mold and hardened.

FeS 24 was formed by the same method as in the first example.

A thin plate of pure iron and a thin plate of platinum was used as cathode 25 and anode 21 respectively. Each constituent element was arranged and contacted as shown in FIG.6, and tightened from outside to complete the assemblage of the device.

The power generation performance (under operation temperature of 44 47 C) of the device thus prepared is shown in Table 9.

(Table 9) Breakaway voltage 0.74 V Ld Attenuation Load ta Output(mW) after continuous generation for 2 Hrs.

0.02 No attenuation S Industrial applicability As cited above, according to the present invention, the conversion of thermal energy to electric power is possible with high thermal efficiency.

The thermoelectric power generation body according to the present invention uses the electric potential of electrochemical reaction as source of function and is of compact

"SSS

construction with less wear and easy maintenance.

S

too%* Moreover, semiconductors suitable for mass production are Sused, which is beneficial to general purpose use of the thermoelectric power generation body of the present invention.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

34 S 55 5.5 5 5 Q:op lgcpI<2756cdoc4-04IO4 34A Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. A thermoelectric power generator comprising a thin plate of solidified fine and hydrated particles of a sulfide semiconductor in contact with an electrochemical reaction having a lower Fermi level on a side and in contact with an electrochemical reaction having a higher Fermi level on an opposite side, wherein the electrochemical reaction having the lower Fermi level is a first solidified redox reaction system comprising an aqueous solution of {Cu+(NH 3 2 ~Cu2+ (NH 3 2 2) or Ni2+ (NH 3 )6 carried on electrically conductive adsorbent and bound with hydrophilic organic polymer and hemihydrated gypsum.

2. A thermoelectric power generator according to claim 1, wherein the sulfide semiconductor plate consists of a single n-type or single p-type sulfide semiconductor.

3. A thermoelectric power generator according to claim 1, oo S 20 wherein the sulfide semicnductor plate comprises an aniso type hetero junction between a p-type sulfide semiconductor located in the anode side and a n-type sulfide semiconductor located in the cathode side. 25

4. A thermoelectric power generator according to claim 1, S. wherein the first solidified redox reaction system is composed so that rate controlling steps of an electron transfer are a reaction at an interface between the first solidified redox reaction system and the sulfide semiconductor plate, and conduction through the conductive adsorbent.

Q. 0fpcpU276cdoc-04M/S4 36 A thermoelectric power generator according to claim 4, wherein the adsorbent of the first solidified redox reaction system comprises an adsorptive constituent and an electron conducting and chemically stable constituent.

6. A thermoelectric power generator according to claim wherein the adsorptive constituent is selected from the group consisting of active carbon, charcoal, silica gel, hemihydrated gypsum, molecular sieve, and soccer ball-like carbone, and the electron conductive constituent is selected from the group consisting of platinum, gold and graphite.

7. A thermoelectric power generator according to claim 1, further comprising: a second solidified redox reaction system, having a direct connection on a side with the first solidified redox reaction system; an anode in contact with the second solidified redox reaction system; and 20 a n auxiliary electrode sandwiched etween and in contact with the first and second solidified redox reaction systems, wherein a reaction H 2 0+-O 2 +2e-20H, being effective to sustain the lower Fermi level of the redox reaction, is kept in the state of dynamic balance by cooperation of the 25 anode and the auxiliary electrode for oxidation.

8. A thermoelectric power generator according to claim 1, o further comprising a cathode in contact with the sulfide semiconductor plate, wherein the cathode is composed of a metal selected from the group consisting of Fe, Ni, Cu and brass, and wherein the sulfide semiconductor plate further comprises at least an effective amount of water or glycerol Q.U 42756c doc-4/104 37 in order to generate a high Fermi level in the equilibrium reaction.

9. A thermoelectric power generator according to claim 1, wherein the hydrated fine particles of sulfide semiconductor are selected from the group consisting of Cu 2 S, FeS, Fe 2 S 3 NiS, coprecipitated FeS-NiS and coprecipitated FeS.ZnS, wherein said particles are synthesised by an ionic reaction between a constituent cation in the form of chloride or sulfate and S 2 in the form of aqueous solution of 10~20 wt% of potassium sulfide or sodium sulfide at an equivalence ration of S 2 to cation between 0.85 to 1.1, and wherein the ionic reaction produces a colloidal slurry of sulfide semiconductor particles.

A thermoelectric power generator according to claim 9, wherein the colloidal slurry of sulfide semiconductor :particles synthesised by ionic reaction in aqueous solution Sis solidified into a thin plate by adding binders to the 20 aqueous solution, supporting the solution on a plurality of sheets of liquid absorbing paper, layering the plurality of the sheets, and drying the plurality of sheets.

11. A thermoelectric power generator according to claim *e 25 wherein the binders are selected from the group consisting *g of hemihydrated gypsum and hydrophilic organic polymer. *o* Q.aprM275k dcM."U4Jv 38

12. A thermoelectric power generator substantially as hereinbefore described with reference to the accompanying drawings. DATED this 4th day of August, 2004 SHIN-ETSJ CHEMICAL CO., LTD., NITCHIRO HASEGAWA AND MUTSUKO HASEGAWA By their Patent Attorneys DAVIES COLLISON CAVE o 0 a a S a a a. a S S. a a a a a